Cubic boron nitride is a known industrial abrasive. It is produced from hexagonal boron nitride, hBN, at high pressures and temperatures, very often under the influence of Mg, Li, Mg.sub.3 N.sub.2 and Li.sub.3 N as flux (catalyst), as described, for example, in U.S. Pat. No. 2,947,617. To obtain the cubic form of boron nitride, this crystal structure must be favored. This occurs on the one hand by the addition of selected active catalysts based on alkali metals, alkaline earth metals, lead, tin, antimony, or nitrides of these metals, and the like, and on the other hand by a directed slow cooling of the melt which favors the crystal growth. Typical crystal morphology for cBN is octahedral or tetrahedral. Typical crystal sizes range from about 20 up to 500 .mu. (0.02-0.5 mm), dependent on the production conditions.
Hexagonal boron nitride is used in industry in pressed and sintered bodies as a powder, paste or spray, e.g., to produce or line casting molds or also as a lubricant, as a temperature-resistant shaped material.
Cubic boron nitride, which is distinguished from hexagonal boron nitride by its higher temperature resistance and by its hardness, which lies only slightly below that of diamond, finds a use as a cutting grain in the tool and abrasive industry. A further form of boron nitride is known under the name "turbostratic boron nitride, tBN". It is used as a starting material for pressed bodies and for the production of cubic boron nitride.
In addition to these, up to now there has only been a so-called "amorphous boron nitride", synthesized by Sumiya et al., see Materials Research Bulletin, 18, pages 1203-1207, 1983; it is termed aBN-1 below, for the soft phase produced at normal atmospheric pressure. This aBN-1 is a boron nitride which no longer possesses any graphite-like layer structure, but consists of fragments of crystal lattice and is soft. Thus it is not established whether aBN-1 is really amorphous or whether it is only present in a finely-powdered state.
A suitable apparatus for producing the pressures and temperatures in order to produce cubic boron nitride from hexagonal boron nitride is described, for example, in U.S. Pat. No. 2,941,243.